The present invention relates to an X-ray diffraction method and an X-ray diffraction apparatus with the use of the parallel beam method.
In the powder X-ray diffraction method for powder samples, thin film samples or polycrystalline samples, an analyzer must be inserted into a diffracted-beam-side optical system (i.e., a receiving optical system) in order to improve the angular resolution when using the parallel beam method. One of known analyzers is a long parallel slit that has a narrow angle of X-ray aperture, and the other is an analyzer crystal. The method with the long parallel slit is not so severe in X-ray intensity reduction but is inferior in angular resolution. On the contrary, the method with the analyzer crystal is superior in angular resolution but is severe in X-ray intensity reduction. Therefore, in the parallel beam method, there is desired a suitable analyzer that is superior in angular resolution and is small in X-ray intensity reduction.
An improvement in using the analyzer crystal and preventing the radiation intensity reduction in totality is known as disclosed in Journal of Synchrotron Radiation (1996), 3, 75-83 (which will be referred to as the first publication hereinafter) and Journal of Research of the National Institute of Standards and Technology, 109, 133-142 (2004) (which will be referred to as the second publication hereinafter).
The first publication discloses that plural (for example, six) X-ray detectors (which are scintillation counters) are located around a sample in the powder diffraction method using synchrotron orbit radiation. An analyzer crystal made of a Ge(111) flat plate is inserted between the sample and each of the X-ray detectors. The use of the plural X-ray detectors enables a short-time measurement of a diffraction pattern with a predetermined angular range as compared to the case using a single X-ray detector. Accordingly, the X-ray intensity reduction caused by the use of the analyzer crystals is prevented in totality of the apparatus.
The second publication discloses that, as well as the first publication, plural (for example, nine) analyzer crystals and as many X-ray detectors (scintillation counters) are located around a sample in the powder diffraction method.
By the way, the present invention is concerned with the use of a mirror having a reflective surface shaped in an equiangular spiral (a logarithmic spiral) in an X-ray diffraction apparatus with the parallel beam method. On the other hand, as to an X-ray diffraction apparatus with the focusing beam method, the use of a mirror (analyzing crystal) having an equiangular spiral reflective surface is disclosed in Japanese Patent Publication No. 6-82398 A (1994) (which will be referred to as the third publication hereinafter), Japanese Patent Publication No. 7-63897 A (1995) (which will be referred to as the fourth publication hereinafter), and Japanese Patent Publication No. 7-72298 A (1995) (which will be referred to as the fifth publication hereinafter).
The third publication discloses an analyzer crystal, which has a reflective surface shaped in a logarithmic spiral. The analyzer crystal is made of a synthetic multilayer lattice, in which the farther a point on the reflective surface is away from the X-ray source, the larger the lattice spacing is. The fourth publication discloses an X-ray spectrometer according to the second embodiment, which is composed of a combination of plural flat elements. Each flat element has a reflective point located on a curve that is nearly a logarithmic spiral. Each flat element is made of a synthetic multilayer lattice, in which the farther a point on the reflective surface is away from the X-ray source, the larger the lattice spacing is. The fifth publication discloses an X-ray spectroscopic element according to the fourth embodiment, which is composed of a combination of curved reflective surfaces with steps therebetween, each reflective surface having a longitudinal cross section close to a logarithmic spiral curve. Each reflective surface is made of a synthetic multilayer lattice, in which the farther the reflective surface is away from the X-ray source, the larger the lattice spacing is.
The structure that places plural analyzer crystals and plural X-ray detectors around a sample as disclosed in the first and second publications is so complex and expensive that it is hardly applicable to an X-ray diffraction method in a laboratory system.
The mirror having a reflective surface with a variable lattice spacing as disclosed in the third, fourth and fifth publications can not be used as a mirror, in the parallel beam method, for reflecting an X-ray beam having a different incident angle toward a different place.